<template>
  <ul class="list">
      <li class="item" 
        v-for="(item,key) of letters" 
        :key="key" 
        @click="handleLetterClick"
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        :ref="item"
    >{{item}}</li>
  </ul>
</template>

<script>
import Bscroll from 'better-scroll'
export default {
  name: "CityAlphabet",
  props: {
      cities:Object
  },
  computed: {
    letters () {
        const letters = []
        for (let i in this.cities) {
            letters.push(i)
        }
        return letters
    }  
  },
  data () {
      return {
        touchStatus: false,
        startY:0,
        timer:null
      }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop  
  },
  methods: {
      handleLetterClick (e) {
          this.$emit('change',e.target.innerText)
      },
      handleTouchStart(){
          this.touchStatus = true
      },
      handleTouchMove(e){
          if (this.touchStatus) {
              if(this.timer){
                  clearTimeout(this.timer)
              }
              this.timer = setTimeout(() => {
                  const touchY = e.touches[0].clientY - 79
                  const index = Math.floor((touchY - this.startY) / 20) 
                  if(index >= 0 && index < this.letters.length){
                    this.$emit('change',this.letters[index])
                  }
              },16)
          }
      },
      handleTouchEnd(){
          this.touchStatus = false
      }
  }
}
</script>
<style lang="stylus" scoped>
@import '~styles/varibles.styl'
.list
    position absolute
    top 1.58rem
    right 0
    bottom 0
    width .4rem
    display flex
    flex-direction column
    justify-content center
    .item
        line-height .4rem
        text-align center
        color $bgColor
</style>

